An ability to detect, localize, and identify living organisms and monitor their activities has many uses. Biological attacks caused by wood destroying fungus, borers, termites, carpenter ants and the like are a major problem for structures made wholly or partially of wood. Such attacks can cause considerable damage to wooden structures. The detection and localization of active infestation of termites, ants, and other insects could substantially improve treatment outcome. The detection and monitoring of human activities gives the invention utility as a potential rescue system when it is used in the search for unconscious subjects who may be injured. The invention can also be used as intrusion and stowaway detection; it can help military forces clear a building when people may be concealed in interior hiding places. The invention will enable Special Weapons and Tactics (SWAT) or Special Operations Response Team (SORT) team commanders to better visualize hostage situations. Another equally important use of the invention is in law enforcement including police enforcement and management of correction institutions to detect and monitor offenders through structural walls.
Commonly used methods for detection of living organisms are mostly based on visual observations using human eyes or optical cameras. However if a partition obstructs the view visual approach does not work. Microwave, RF or acoustic signals can penetrate through a structure or partition thus offering an opportunity to detect living organisms within or behind it. This approach is known as Though Wall Sensing, or TWS. The sensing of living organisms' activities is based on their motion. The microwave, RF or acoustic TWS system is capable of detecting extremely small motions allowing for detection of living (moving) organisms in otherwise static environment. Conversely with the detection of insects in a wall, in the case where the invention is used to detect living organisms behind a structure or partition, the signals can be filtered to eliminate indications within a wall or structure to show the presence of living organisms on the other side of the structure or wall.
Prior art relevant to TWS are utilizing effects of Doppler or phase fluctuation due to motion of a target or echo-location of a target coupled with monitoring of target's position.
U.S. Pat. No. 3,754,254 to Jinman (the “Jinman '254 Patent”) discloses a device for detecting moving targets by the Doppler shift of radiation reflected or scattered by a target that is illuminated by transmitted radiation. The Jinman '254 Patent focused on the problem of an interfering signal having a frequency difference from the transmitted radiation lying in the range of the expected Doppler shift, which would give a false target indication. The Jinman '254 Patent discloses that modulating the frequency of the transmitted radiation can mitigate such problem, so that the scattered or reflected radiation has a coherence with the transmitted radiation. The Jinman '254 Patent further discloses that a device performing the aforesaid function is particularly applicable to intruder alarm systems.
U.S. Pat. No. 6,313,643 to Tirkel (the “Tirkel '643 Patent”) has been distinguished from the invention disclosed by the Jinman '254 Patent on the basis that the termite detection system disclosed therein includes a transmitter adapted to transmit a “near field” microwave signal into a structure and a receiver adapted to receive reflected signals that are indicative of the presence of insects in the “near field” of the microwave signal. However, the Tirkel '643 Patent does not disclose that the termite detection system is able to detect the presence of termites within the “far field” of the signal generated thereby. As a result, the termite detection system's function is substantially constrained. In addition, the Tirkel '643 Patent does not disclose whether the termite detection system is able to distinguish output signals indicative of the presence of termites in a structure and output signals caused by movement of the termite detection system itself. As a result, it would be difficult for an operator of the termite detection system disclosed by the Tirkel '643 Patent to distinguish false indications of the presence of insects in a structure from the actual presence of insects therein and, therefore, could lead to increased time and costs for testing a structure and/or inaccurate test results.
Recently developed TWS techniques to sense the location of a human subject inside of a room from the outside of that room is described in Hunt, A., Tillery, C., and Wild, N., “Through-the-Wall Surveillance Technologies,” Corrections Today, Vol. 63, No. 4, July 2001. Thus, Greneker, et al. has developed so-called “RADAR Flashlight” which operates at X-band frequency range (near 10 GHz) and employs a CW homodyne radar configuration. (Greneker, E. F., “Radar Sensing of Heartbeat and Respiration at a Distance with Security Applications,” Proceedings of the SPIE, Radar Sensor Technology II, Volume 3066, April 1997; Geisheimer, J. L., Marshall, W. S., and Greneker, E. F. “A continuous-Wave CW Radar for Gait Analysis,” 35th IEEE Asilomar Conference on Signals, Systems and Computers, vol. 1, 2001, pp 834–838; Greneker, Geisheimer, J. “RADAR Flashlight Three Years Later: An Update on Developmental Progress,” Proceedings of the 34th Annual International Carnahan Conference on Security Technology, Ottawa, Canada, October 2000).
Other reported developments are based on wide-band (pulse) technology working similar to echo-locating radars there presence and position of the target based on intensity and time-of-flight of reflected RF pulses. McEwan, T. E. “Ultra-wideband radar motion sensor”, U.S. Pat. No. 5,361,070, discloses motion sensor based on ultra-wideband (UWB) radar technology. UWB radar range is determined by a pulse-echo interval. For motion detection, the sensors operate by staring at a fixed range and then sensing any change in the averaged radar reflectivity at that range. A sampling gate is opened at a fixed delay after the emission of a transmit pulse. The resultant sampling gate output is averaged over repeated pulses. Changes in the averaged sampling gate output represent changes in the radar reflectivity at a particular range, and thus motion.
Other prior art, Barnes et al., “Wide area time domain radar array” U.S. Pat. No. 6,218,979, describes a system and method for high resolution radar imaging using a sparse synchronized array of time modulated ultra wideband (TM-UWB) radars. Two or more TM-UWB radars are arranged in a sparse array. Each TM-UWB radar transmits ultra wideband pulses that illuminate a target, and at least one receives the signal returns. The signal return data is processed according to the function being performed, such as imaging or motion detection.
There is other prior art that utilizes a synchronized array of transmitters and/or receivers for coherent processing of reflected signals, such as described by Geisheimer, et al., Phase-based sensing system, U.S. Pat. No. 6,489,917.
Although significant resources have been devoted to development of practical and commercially viable TWS systems, so far these efforts produced mostly demonstrational or experimental prototypes which are difficult and impractical to employ for real world applications. One of the reasons is that none of the referred prior art is able to distinguish one type of living organism from another: for example to distinguish termite related activity in a wall from moving people that pass behind the same wall. The prior art can't differentiate between insect and human.
In addition, there is no known-living organisms detection device that is able to distinguish motion signals indicative of the presence of living organisms in a structure and signals caused by movement of the device itself. Since electronic insect detection devices typically contain sensitive components designed to detect the movement of insects, any movement of these devices can lead to the false indication of the presence of living organisms in a structure. For instance, hand tremors of an operator holding a living organism detection device cause significant movement thereof. In addition, if a living organism detection device is placed against a structure to be tested, structural vibrations caused by wind, appliances or nearby moving vehicles can lead to the movement of the detection device. Also, moving vehicles that pass behind a structure undergoing testing can cause motion signals that can lead to false indications of the presence of living organisms in a structure. As a result, it would be difficult for an operator of a living organism detection device to distinguish false indications of the presence of living organisms in a structure from the actual presence of living organisms therein.
Accordingly, what would be desirable, but has not yet been developed, is a reliable practical device and method for detecting, localization, monitoring, and differentiating living organisms inside structures, within or behind walls and other partitions.